The omission of radiation therapy (RT) in elderly women with stage 1 estrogen-receptor positive (ER+) breast cancer receiving endocrine therapy (ET) is an acceptable strategy based on randomized trial data. Less is known about the omission of ET +/- RT.
We analyzed SEER-Medicare data for 13,321 women ≥ 66 years with stage I ER+ breast cancer from 2007-2012 who underwent breast conserving surgery. Patients were classified into 4 groups: 1) ET+RT (reference) 2) ET alone (ET), 3) RT alone (RT) and 4) neither RT nor ET (NT). Second breast cancer events (SBCE) were captured using Chubak’s high-specificity algorithm. We used Chi-square tests for descriptive statistics, multivariable multinomial logistic regression to estimate relative risks (RR) of undergoing a treatment, and multivariable, propensity-weighted competing-risks survival regression to estimate standardized hazard ratio (SHR) of SBCE. We set significance at p≤0.01.
Most women underwent both treatments, with 44% undergoing ET+RT, 41% RT, 6.6% ET, and 8.6% NT but practice patterns varied over time: from 2007-2012, RT decreased from 49% to 30%, whereas ET and ET+RT increased (ET: 5.4% to 9.6%; ET+RT: 38% to 51%). Compared to patients 66-69 years, patients 80-85 years were more likely to receive NT (OR=8.9), RT (OR=1.9), or ET (OR=8.8) vs. ET+RT (p<0.01).3% of subjects had an SBCE (2.2% ET+RT, 3.0% RT, 3.2% ET, 7.0% NT). Relative to ET+RT, NT and ET were associated with higher SBCE (NT: SHR 3.7, p<0.001; ET: SHR 2.2, p=0.008)), whereas RT was not associated with a higher SBCE (SHR 1.21, p=0.137). Clinical factors associated with higher SBCE were HER2 positivity and pT1c (SHR 1.7, p=0.006).
Treatment with RT alone in older women with stage I ER+ disease is decreasing. RT alone is not associated with an increased risk for SBCE. By contrast, NT and ET are both associated with higher SBCE in multivariable analysis with propensity weighting. Further study of the omission of endocrine therapy in this patient population is warranted.
Copyright © 2021. Published by Elsevier Inc.
Radiation without endocrine therapy in older women with stage I estrogen-receptor (ER) positive breast cancer is not associated with a higher risk of second breast cancer events.
